Laminated transformer core



E. A. NEYDLI Aug. 10, 1965 Filed June 2-, 1961 INVENTOR. [bu 4R0 10.447014 FIG.4

BY Fm FIG.2

United States Patent 3,200,358 LAMINATED TRANSFORMER CORE Edward A. Neydli, Watertown, Wis.,.assignor to Basic Products Corporation, Milwaukee, Wis., a corporation of Wisconsin Filed June 2, 1961, Ser. No. 114,395 2 Claims. (Cl. 336-217) The present invention relates to magnetic core structures for electrical induction apparatus such as transformers, reactors and the like.

In the usual construction for magnetic cores, the lamnat-ions are cut or punched from relatively large stock sheets which are produced by rolling from bars or billets of a suitable magnetic material, such as various steel alloys such as silicon steel or magnetic nickel iron steel.

' ,It is known that the rolling process produces a grain 1 structure in sheets which may extend in the direct-ion in which the sheets have been rolled. It is further known that the path of leastmagnetic resistance of such a magnetic material is generally in the direction that the sheets have been rolled, though in certain types of steels the most favorable of magnetic directions, insofar as low flux losses are concerned, may be at some angle with respect to the direction of rolling. Thus it will be seen that for optimum results for magnetic cores, it is desirable to cut the laminations from the sheets of magnetic material so that the core flux path is parallel with the path of least magnetic resistance, or parallel with the direction of rolling, even at the corners.

It is known to provide mitered joints at the corners of a laminated sheet metal core, and to overlap adjacent joints so that the magnetic reluctance at the joints is a minimum.

Where punched or cut elements are employed to make up successive laminations, burrs often occur along the cut edges which often combine in successive laminations,

1 particularly at the center leg of a three-legged core, to

provide a complete conductive path between adjacent laminations in which induced currents develop, consequently providing eddy current losses within the transformer or reactor, thereby decreasing their efliciency materially.

The principal object of this invention is to provide a laminated magnetic core construction in which no eddy current losses will develop by virtue of burrs forming a closed conductive path between adjacent laminations.

Another object of the invention is to provide such a magnetic core construction in which the elements forming the laminations are cut from a strip of suitable steel of constant widths which is coated on its top and bottom surfaces and may be coated along its longitudinal edges.

Still another object of the invention is to provide such a laminated core in which the elements of the laminations are cut from strip stock so that only their transverse diagonal and rigth angle transverse edges can have burrs.

In one aspect of the invention, a strip of grain-oriented sheet steel having suitable characteristics may be stress relief annealed and coated on its outside including its longitudinal edges with a core-plate oxide or the like. Trapezoidal elements may be sheared from the strip, and they are shown as having sheared edges of 90 and 45 transversely of the strip. It is to be understood that 60 and 30 or other combinations of end edges may be provided instead of 45 edges to form 90 corners if desired. The dimensions of these elements may be such that when assembled into the form of a three-legged magnetic core, with alternate laminations reversely laid, each of the four outer corners comprises mitered edges that overlap each other in successive laminations so that a minimum of resistance to flux fiow by virtue of air gaps is present.

3,200,358 Patented Aug. 10, 1965 In another aspect of the invention, the intermediate leg of a lamination may comprise a right angular end that may have a burr on it abutting against the inside longitudinal coated edge of a leg of the lamination. The other end of the intermediate leg may have a single 45 transverse edge that may have a burr on it, and the other leg of the lamination that cooperates with it may comprise two elements, each of which has transverse edges that may includeburrs, but the one which contacts the longitudinal coated edge of the intermediate leg prevents the formation of a closed conducting path'within which induced currents can flow if alternate laminations are reversely stacked.

The above, other objects and novel features of the magnetic core will become apparent from the following specification and accompanying drawing which is merely exemplary.

In the drawing:

FIG. 1 is a stacked laminated magnetic core to which the principles of the invention have been applied;

FIG. 2 is a strip of coated steel from which the elements forming the laminations in FIG. 1 are sheared, cut or punched;

FIG. 3 is a view of the arrangement of elements forming the odd numbered laminations;

FIG. 4 is a view of the arrangement of elements forming the even numbered laminations; and

FIG. 5 is a perspective view of a cruciform transformer core.

Referring to the drawing, and particularly to FIGS. 3 and 4, each succeeding lamination may include six elements 10, 11, 12, 13, 14 and 15 which are arranged differently. The side legs 11 and 12 may make perfect The intermediate leg 13, having a cut right angular transverse end 18, may abut the inner coated edge of the legs 10. The opposite end of the leg 13 may have a mitered 45 diagonal cut edge 19, and it may extend through and beyond the leg opposite leg 10. Accordingly, this opposite leg comprises two elements 14 and 15. The element 14 (FIG. 3) is arranged so that its mitered 45 cut edges 20 and 21 converge inwardly. The mitered cut edge Z0 abuts a 45 mitered cut edge 22 of the leg 12 in a manner to provide a notch 23. The mitered cut edge 21 abuts the mitered cut edge 19 of leg 13 in a intanner to provide a notch 24 for a purpose to be described a er.

The element 15 may include a transverse cut edge 25 that abuts a coated edge 26 of the leg 13; and

mitered cut edge 27 that abuts a 45 mitered cut edge 23 of leg 11 in a manner to provide a notch 29. All of the odd numbered laminations are identical with the arrangements of elements 10 to 15, inclusive, as shown in FIG. 3.

Referring to FIG. 4, the arrangement of the elements 10 to 15, inclusive, is produced by turning each element face over, positioning the cross legs 10, 14 and 15 opposite to their positions shown in FIG. 3. The arrangement shown in FIG. 4 is the same for all of the even numbered laminations.

As previously explained, all of the 90 and 45 transverse edges of the elements 10 to 15, inclusive, may have burrs thereon incident to the shearing, cutting or punching action. All other edges of these elements as well as the top and bottom surfaces may be core coated. Accordingly, by making a stack of the laminations having elements 10 to 15 as shown in FIGS. 3 and 4, such that the odd numbers correspond to the arrangement of FIG. 3 and the even numbers correspond to the arrangement of FIG. 4, each mitered edge 16, 17, 22 and 28 of the odd numbered laminations will not register with such mitered edges of the even numbered laminations. This will produce a dual function in that any air gap at these joints will be minimized, and any burrs along these cut edges will not form a closed conducting or magnetic circuit within which induced eddy currents will be generated and successive layers of laminations will be effectively insulated from each other.

Furthermore, it is evident that the cut edges 19, 21

which may be burred cannot provide, with cut edges 18 and 25, a closed conducting circuit within which induced eddy currents will be generated.

Referring to FIG. 2, a strip of magnetic material 30 of constant width may be provided with a core-coating oxide over its entire top, bottom and edges. By designing a single cutter, the six elements may be cut from the currents would be generated.

Referring to FIG. 5, a cruciform type of core may comprise a centrally disposed set of laminations 31 made from elements substantially like elements to 15, and alternately stacked as previously described. Two other sets of laminations 32 and 33 may be arranged on each face of the set 31 to provide a cruciform construction. The dimensions of the elements comprising sets 32 and 33 may be diiferent from the dimensions of the elements forming set 31, and in the embodiment of FIG. 5, the elements of sets 32 and 33 are shown as being somewhat smaller than those forming set 31. 7

Although the various features of the new and improved magnetic core have been shown and described in detail to fully disclose one embodiment of the invention, it will be evident that changes may be made in such details and certain features may be used without others without departing from the principles of the invention.

What is claimed is: g

1;. In a magnetic core construction of stacked laminae comprising a plurality of identical laminations oppositely arranged relative to each other, each lamination comprising spacedparallel end legs, each end leg having mitered ends; a one-element cross leg for each lamination being mitered at each end thereof, each cross leg mitered end mating with a corresponding mitered end of each of said end legs; a center leg having one square end abutting the one-element cross leg and the other end mitered; and a two-element cross leg completing said lamination, one of the elements of said two-element cross leg having both ends mitered to abut corresponding mitered ends on one of said end legs and said center leg, and the other element having one square end abutting with said center leg and the other end mitered to abut with a corresponding mitered end of the other of said end legs, said two-element cross leg being offset outwardly in the plane of'its lamination away from said one-element cross leg so that all the mitered ends of said two-element cross leg are offset from the respective abutting mitered ends of said end legs and said center leg, the offset mitered end of said other element of said two-element cross leg forming a notch at the inner extremity of the abutting mitered leg of an end leg, one offset mitered end of said one-element of said two-element cross leg forming a notch at the inner extremity of the abutting mitered end of an end leg and the other offset mitered end of said one-element forming a notch at the inner extremity thereof adjacent said center 1 leg, said laminations being turned relative to each other so that the mitered end of the center leg of one lamination and the notch formed adjacent thereto rests on a one-element cross leg of the next adjacent lamination.

2. In a magnetic core construction of stacked laminae as claimed in claim 1 and further comprising a central stack of laminae and separate stacks of laminae on both sides of said central stack with the laminae of all said stacks having similar construction, the mitered ends of the center legs forming points which extend outwardly beyond the outer edges of the two-element cross leg of the respective laminae, the dimensions of the legs within the central stack being different from the dimensions of the legs within the side stacks.

References Cited by the Examiner UNITED STATES PATENTS JOHN F. BURNS, Primary Examiner.

MILTON o. HIRSHFIELD, Examiner. 

1. IN A MAGNETIC CORE CONSTRUCTION OF STACKED LAMINAE COMPRISING A PLURLITY OF IDENTICAL LAMINATION OPPOSITELY ARRANGED RELATIVE TO EACH OTHER, EACH LAMINATION COMPRISING SPACED PARALLEL END LEGS, EACH END LEG HAVING MITERED ENDS; A ONE-ELEMENT CROSS LEG FOR EACH LAMINATION BEING MITERED AT EACH END THEREOF, EACH CROSS LEG MITERED END MATING WITH A CORRESPONDING MITERED END OF EACH OF SAID END LEGS; A CENTER LEG HAVING ONE SQUARE END ABUTTING THE ONE-ELEMENT CROSS LEG AND THE OTHER END MITERED; AND A TWO-ELEMENT CROSS LEG COMPLETING SAID LAMINATION, ONE OF THE ELEMENT OF SAID TWO-ELEMENT CROSS LEG HAVING BOTH ENDS MITERED TO ABUT CORRESPONDING MITERED ENDS ON ONE OF SAID END LEGS AND SAID CENTER LEG, AND THE OTHER ELEMENT HAVING ONE SQUARE END ABUTTING WITH SAID CENTER LEG AND THE OTHER END MITERED TO ABUT WITH A CORRESPONDING MITERED END OF THE OTHER OF SAID END LEGS, SAID TWO-ELEMENT CROSS LEG BEING OFFSET OUTWARDLY IN THE PLANE OF ITS LAMINATION AWAY FROM SAID ONE-ELEMENT CROSS LEG SO THAT ALL THE MITERED ENDS OF SAID TWO-ELEMENT CROSS LEG ARE OFFSET FROM THE RESPECTIVELY ABUTTING MITERED ENDS OF SAID END LEGS AND SAID CENTER LEG, THE OFFSET MITERED END OF SAID OTHERE ELEMENT OF SAID TWO-ELEMENT CROSS LEG FORMING A NOTCH AT THE INNER EXTREMITY OF THE ABUTTING MITERED LEG OF AN END LEG, ONE OFFSET MITERED END OF SAID ONE-ELEMENT OF SAID TWO-ELEMENT CROSS LEG FORMING A NOTCH AT THE INNER EXTREMITY OF THE ABUTTING MITERED END OF AN END LEG AND THE OTHER OFFSET MITERED END OF SAID ONE-ELEMENT FORMING A NOTCH AT THE INNER EXTREMITY THEREOF ADJACENT SAID CENTER LEG, SAID LAMINATIONS BEING TURNED RELATIVE TO EACH OTHER SO THAT THE MITERED END OF THE CENTER LEG OF ONE LAMINATION AND THE NOTCH FORMED ADJACENT THERETO RESS ON A ONE-ELEMENT CROSS LEG OF THE NEXT ADJACENT LAMINATION. 